There is increasing evidence from studies in humans and laboratory animals that exposing the skin to UV radiation can modify certain immune reactions, both locally in the irradiated skin and systemically. UV irradiation of mice can activate the suppressor cell pathway of the immune response to antigens that induce delayed and contact hypersensitivity reactions. These findings raise the question of whether exposure to UV radiation can also induce suppressor cells to microbial and viral antigens, and thus interfere with the ability of the immune system to resist and eliminate infectious agents. The purpose of these studies is to investigate the effects of UV irradiation on the pathogenesis of infectious diseases. The hypothesis to be tested is that exposure of mice to UV-B radiation alters immunity to infectious agents, thereby increasing the incidence and severity of infection. Initial studies will determine the effects of UV-B radiation on resistance to fungal infection using Candida albicans in inbred mice. The effects of UV irradiation on delayed hypersensitivity, antibody production, and suppressor cell formation to candida antigens will be assessed, in addition to the effects on lethality and persistence of infection. Additional studies will address similar questions using Herpes Simplex Virus type 1. If UV irradiation interferes with resistance to infection, the immunologic and physiologic mechanisms involved will be determined and the specific wavelengths of UV radiation responsible for the effect will be identified. In addition, animal models will be developed for investigations of diseases produced by Mycobacteria and Listeria.